Transcript for White House Acknowledges Evidence of Chemical Weapons in Syria

We'll turn now to the other disturbing headline breaking today in syria and early evidence that country has used chemical weapons now against its own people. What now from from the u.S. And how convinced is the white house that that evidence can be believed? Martha raddatz is live in washington. Good evening. Reporter: This is the closest the u.S. Has ever come to saying the syrian government has crossed that red line, which means this is the closest america has come to having to consider military action in syria. It is a stunning assessment. American intelligence now believing that the syrian regime has used chemical weapons on a small scale on its own people. They have a reasonable amount of confidence that some amount of chemical weapons was used. Reporter: Specifically sarin. The nerve agent suspected in an attack in march, leaving 30 dead. Sarin acts in seconds, causing convulsions and paralysis that suffocates its victims. President obama hasn't wanted to regime, if it ever used chemical weapons, that would change. I have made clear that the use of chemical weapons is a game-changer. Reporter: On capitol hill today, the call for action was swift. I think it's pretty obvious that red line has been crossed. Reporter: But today the white house made clear that despite the initial evidence, they want certainty first, an investigation to establish incredible and corroborated facts. And we all heard what said moments ago. This is the closest yet the u.S. Has been to debating any kind of military action. But kind of action could they be considering? David, you could set up a flow-fly zone, stopping syria's air force from attacking its people. You could attack syrian military targets. And there are pleant of fire power in the region. We also have 250 soldiers right now in jordan to dealing with planning, to secure chemical weapons if that becomes necessary. But I think the u.S. Would think long and hard before taking any military action in syria. It is a complicated place. All right, martha, thank you.

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